What forms do seismic hazards take, what determines their impact, and how can they be managed?
The nature of seismicity and its relation to plate tectonics; forms of seismic hazard including earthquakes, tsunamis, liquefaction and landslides; primary and secondary impacts; and prediction, prevention, protection and adaptation.
A focused answer to the AQA A-Level Geography 3.1.5 content on seismic hazards, covering the nature of seismicity and its link to plate tectonics, the forms of seismic hazard including earthquakes, tsunamis, liquefaction and landslides, the primary and secondary impacts, and management responses.
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What this dot point is asking
AQA section 3.1.5 wants you to explain the nature of seismicity and its tectonic causes, the forms of seismic hazard (earthquakes, shockwaves, tsunamis, liquefaction, landslides), the primary and secondary impacts, and the management responses. The recurring exam theme is that development and context, not just magnitude, determine how deadly an earthquake is.
The nature of seismicity
Earthquakes occur when accumulated stress along a fault or plate margin is released suddenly, sending out seismic waves from the focus; the point directly above is the epicentre. The margin type sets the profile: constructive margins give shallow, low-magnitude quakes; destructive margins give the deepest and most powerful quakes along the Benioff zone; conservative margins give shallow but often powerful quakes (San Andreas). Magnitude is measured on the moment magnitude scale, and shaking intensity on the modified Mercalli scale.
Forms of seismic hazard
- Ground shaking (shockwaves): the primary hazard, collapsing buildings and infrastructure.
- Tsunamis: a submarine earthquake causes vertical sea-bed displacement, displacing water that travels fast across the deep ocean and shoals into a destructive wall at the coast (Tohoku 2011).
- Liquefaction: saturated, fine sediment shaken until it behaves like a liquid, so buildings sink or tilt (Christchurch 2011).
- Landslides and avalanches: shaking destabilises slopes, burying settlements and blocking valleys.
Impacts
Primary impacts are immediate and direct: building and infrastructure collapse, deaths and injuries from shaking. Secondary impacts follow: tsunamis (often the biggest killer), fires from ruptured gas mains, disease from broken water and sanitation, landslides, economic disruption and homelessness. Impacts span environmental, social, economic and political categories and both short and long term, and they are filtered by development: aseismic construction, early warning, insurance and effective relief sharply cut the toll in wealthier, better-governed places.
Management responses
- Protection: the most reliable tool. Aseismic building design (deep flexible foundations, cross-bracing, base isolation, automatic gas shut-offs) keeps buildings standing; sea walls and evacuation routes reduce tsunami deaths.
- Prediction: precise prediction is not yet possible, but early-warning systems detect the first fast waves and give seconds to minutes of warning (Japan's system); tsunami warning networks give longer notice.
- Prevention: impossible; earthquakes cannot be stopped.
- Adaptation and preparedness: land-use planning away from fault and liquefaction zones, building codes, education and drills, and insurance build resilience over time.
Try this
Q1. Name four seismic hazards. [4 marks]
- Cue. Ground shaking (shockwaves), tsunamis, liquefaction and landslides.
Q2. Explain how liquefaction damages buildings. [3 marks]
- Cue. Shaking causes saturated fine sediment to lose strength and behave like a liquid, so foundations sink or tilt and buildings collapse.
Q3. Explain why aseismic building design reduces earthquake deaths. [3 marks]
- Cue. Flexible foundations, base isolation and cross-bracing let buildings absorb and dissipate shaking without collapsing, the main cause of primary deaths.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 2021 (style)9 marksAssess the extent to which the level of economic development determines the impact of seismic hazards.Show worked answer →
A 9 mark "assess" question (AO1 plus AO2): reach a supported judgement. Development shapes vulnerability and capacity to cope more than the raw hazard. Higher-income places enforce aseismic building codes, run early-warning systems and have insurance, so deaths can be limited even when economic losses are huge (Tohoku, Japan 2011, over 200 billion US dollars). Lower-income places suffer mass casualties from poor construction, weak governance and slow relief (Haiti 2010, over 200,000 deaths).
Then qualify: development is not the only factor. Magnitude, focal depth, time of day, ground conditions (liquefaction in Christchurch 2011), secondary hazards (the Tohoku tsunami caused most deaths) and population density all matter.
Conclude that development is a powerful but not sole determinant. Markers reward a calibrated judgement weighing development against physical and contextual factors with named examples.
AQA 2019 (style)6 marksExplain how a submarine earthquake can generate a tsunami.Show worked answer →
A 6 mark "explain" question (AO1). At a destructive margin, a submarine earthquake causes a sudden vertical displacement of the sea bed (the overriding plate snaps upward after being dragged down). This displaces a huge volume of water.
The displaced water spreads outward as a series of long-wavelength, low-amplitude waves travelling at high speed (up to 700 km/h) across the deep ocean. As the waves reach shallow water near the coast, they slow and steepen (shoaling), the wavelength shortens and the wave height builds rapidly into a destructive wall of water that surges inland.
Markers reward the chain: vertical sea-bed displacement to water displacement to fast deep-ocean travel to shoaling and run-up at the coast. The 2011 Tohoku tsunami is a strong example.
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Sources & how we know this
- AQA A-level Geography (7037) specification — AQA (2016)